1. Field of the Invention
The present invention in general relates to an implantable medical device comprising an hermetically sealed housing which houses an electronic unit and an electrochemical energy storage for supplying electrical current to the medical device. In particular the present invention to a hearing aid.
2. Description of Related Art
The active implants with which the present invention is concerned can be in particular systems for rehabilitation of a hearing disorder as they are further described in the prior art documents referred to in the following.
In recent years rehabilitation of sensorineural hearing disorders with partially implantable electronic systems has acquired major importance. In particular this applies to the group of patients in which hearing has completely failed due to accident, illness or other effects or is congenitally non-functional. If in these cases only the inner ear (cochlea) and not the neural auditory path which leads to the brain is affected, the remaining auditory nerve can be stimulated with electrical stimulation signals and thus a hearing impression can be produced which can lead to speech comprehension. In these so-called cochlear implants (CI) an array of stimulation electrodes which is controlled by an electronic system is inserted into the cochlea. This electronic module is encapsulated hermetically tightly and biocompatibly and is surgically embedded in the bony area behind the ear (mastoid). The electronic system, however, contains essentially only decoder and driver circuits for the stimulation electrodes. Acoustic sound reception, conversion of this acoustic signal into electrical signals and their further processing always take place externally in a so-called speech processor which is worn outside on the body. The speech processor converts the preprocessed signals coded accordingly onto a high frequency carrier signal which via inductive coupling is transmitted through the closed skin (transcutaneously) to the implant. The sound-receiving microphone always is located outside of the body and in most applications in a housing of a behind-the-ear hearing aid worn on the external ear and is connected to the speech processor by a cable. Such cochlear implant systems, their components and the principles of transcutaneous signal transmission are described, by way of example, in published European Patent Application No. 0 200 321 A2 and in U.S. Pat. Nos. 5,070,535, 4,441,210, 5,626,629, 5,545,219, 5,578,084, 5,800,475, 5,957,958 and 6,038,484. Processes of speech processing and coding in cochlear implants are described, for example, in published European Patent Application No. 0 823 188 A1, in European Patent 0 190 836 B1 and in U.S. Pat. Nos. 5,597,380, 5,271,397, 5,095,904, 5,601,617 and 5,603,726.
In addition to rehabilitation of congenitally deaf persons and those who have lost their hearing using cochlear implants, for some time, there have been approaches to offer better rehabilitation than with conventional hearing aids to patients with a sensorineural hearing disorder which cannot be surgically corrected by using partially or totally implantable hearing aids. In most embodiments the principle consists in stimulating via a mechanical or hydromechanical stimulus an ossicle of the middle ear or directly the inner ear, and not via the amplified acoustic signal of a conventional hearing aid in which the amplified acoustic signal is supplied to the external auditory canal. The actuator stimulus of these electromechanical systems is accomplished with different physical transducer principles, such as, for example, by electromagnetic and piezoelectric systems. The advantage of these processes is seen mainly in the sound quality which is improved as compared to conventional hearing aids, and for totally implanted systems, in the fact that the hearing prosthesis is not visible.
Such partially and filly implantable electromechanical hearing aids are described, for example, by Yanigahara and Suzuki et al. (Arch Otolaryngol Head Neck, Surg, Vol. 113, 1987, pp. 869-872; Hoke, M. (ed), Advances in Audiology, Vol. 4, Karger Basel, 1988), Lehner et al.: xe2x80x9cElements for coupling an implantable hearing aid transducer to the ossicles or perilymph by cold deformationxe2x80x9d, in HNO Vol. 46, 1998, pages 27-37; Baumann et al.: xe2x80x9cBasics of energy supply to completely implantable hearing aids for sensorineural hearing lossxe2x80x9d, in HNO Vol. 46, 1998, pp. 121-128; Lehner et al.: xe2x80x9cAn osseointegrated manipulator device for the positioning and fixation of implantable hearing aid transducersxe2x80x9d, in HNO Vol. 46, 1998, pp. 311-323; Lehner et al.: xe2x80x9cA micromanipulator for intraoperative vibratory hearing tests with an implantable hearing aid transducersxe2x80x9d, in HNO Vol. 46, 1998, pp. 507-512; Zenner et al.: xe2x80x9cFirst implantations of a totally implantable electronic hearing system for sensorineural hearing lossxe2x80x9d, in HNO Vol. 46, 1998, pp. 844-852; Leysieffer et al.: xe2x80x9cA totally implantable hearing device for the treatment of sensorineural hearing loss: TICA LZ 3001xe2x80x9d, in HNO Vol. 46, 1998, pp. 853-863; and are described in numerous patent documents, among others in published European Patent Application No. 0 263 254, in commonly owned U.S. Pat. Nos. 5,277,694 and 5,411,467 which are hereby incorporated by reference, as well as in U.S. Pat. Nos. 3,764,748, 4,352,960, 5,015,225, 5,015,224, 3,557,775, 3,712,962, 4,988,333 and 5,814,095.
Many patients with inner ear damage also suffer from temporary or permanent noise impressions (tinnitus) which cannot be surgically corrected and against which up to date there are no approved drug treatments. Therefore so-called tinnitus maskers are known. These devices are small, battery-driven devices which are worn like a hearing aid behind or in the ear and which, by means of artificial sounds which are emitted via for example a hearing aid speaker into the auditory canal, psychoacoustically mask the tinnitus and thus reduce the disturbing noise impression if possible to below the threshold of perception. The artificial sounds are often narrow-band noise (for example, tierce noise) which can be adjusted in its spectral position and its loudness level via a programming device to enable adaptation to the individual tinnitus situation as optimum as possible. In addition, there since recently exists the so-called retraining method in which by combination of a mental training program and presentation of broadband sound (noise) near the auditory threshold in quiet the perceptibility of the tinnitus is likewise supposed to be largely suppressed (H. Knoer xe2x80x9cTinnitus retraining therapy and hearing acousticsxe2x80x9d journal xe2x80x9cHoerakustikxe2x80x9d 2/97, pages 26 and 27). These devices are also called xe2x80x9cnoisersxe2x80x9d.
In the two aforementioned methods for hardware treatment of tinnitus, hearing aid-like, technical devices must be carried visibly outside on the body in the area of the ear; which devices stigmatize the wearer and therefore are not willingly worn.
U.S. Pat. No. 5,795,287 describes an implantable tinnitus masker with direct drive of the middle ear for example via an electromechanical transducer coupled to the ossicular chain. This directly coupled transducer can preferably be a so-called xe2x80x9cFloating Mass Transducerxe2x80x9d (FMT). This FMT corresponds to the transducer for implantable hearing aids which is described in U.S. Pat. No. 5,624,376.
In commonly owned co-pending U.S. Patent applications Ser. Nos. 09/372,172 and 09/468,860 which are hereby incorporated by reference implantable systems for treatment of tinnitus by masking and/or noiser functions are described, in which the signal-processing electronic path of a partially or totally implantable hearing system is supplemented by corresponding electronic modules such that the signals necessary for tinnitus masking or noiser functions can be fed into the signal processing path of the hearing aid function and the pertinent signal parameters can be individually adapted to the pathological requirements by further electronic measures. This adaptability can be accomplished by the necessary setting data of the signal generation and feed electronics being stored or programmed by hardware and software in the same physical and logic data storage area of the implant system, and the feed of the masker or noiser signal into the audio path of the hearing implant can be controlled via the corresponding electronic actuators.
Further systems for masking tinnitus are known for example from German utility model No. 296 16 956, published European Patent Applications Nos. 0 537 385 A1 and 0 400 900 A1, WO 91/17638, W096/00051, WO 90/07251, DE 41 04 359 C2 and from U.S. Pat. Nos. 5,697,975, 5,788,656 and 5,403,262.
For all of the above rehabilitation devices it today appears to be very sensible to design the systems such that they can be implanted completely. Depending on the desired function, such hearing systems are comprised of three or four functional units: a sensor (microphone) which converts the incident airborne sound into an electrical signal, an electronic signal processing, amplification and implant control unit, an electromechanical or implantable electroacoustic transducer which converts the amplified and preprocessed sensor signals into mechanical or acoustic vibrations and sends them via suitable coupling mechanisms to the damaged middle and/or inner ear, or in the case of cochlear implants a cochlear stimulation electrode, and an electric power supply system which supplies the aforementioned modules. Furthermore, there can be an external unit which makes available electrical recharging energy to the implant when the implant-side power supply unit contains a rechargeable (secondary) battery. Especially advantageous devices and processes for charging of rechargeable implant batteries are described in commonly owned co-pending U.S. patent application Ser. No. 09/311,566 and in commonly owned U.S. Pat. No. 5,279,292 which are hereby incorporated by reference. Preferably there can also be a telemetry unit with which patient-specific, audiological data can be wirelessly transmitted bidirectionally or programmed in the implant and thus permanently stored, as was described by Leysieffer et al.: xe2x80x9cA totally implantable hearing device for the treatment of sensorineural hearing loss: TICA LZ 3001xe2x80x9d, in HNO Vol. 46, 1998, pp. 853-863.
In addition to the above fields of application of the present invention, the active implants may also be comprised of other systems for rehabilitation of a bodily disfunction, such as cardiac pacemakers, defibrillators, drug dispensers, nerve or bone growth stimulators, neurostimulators, pain suppression devices, and the like, wherein a secondary, rechargeable, electrochemical cell is used as energy source for operation.
In above incorporated U.S. Pat. No. 5,279,292 there is disclosed an implantable hearing system in which, in accordance with a first embodiment, control electronics for the actuator of the hearing system as well an energy storage which can be recharged from an external transmitter coil via a receiving coil are disposed within an implantable housing. In accordance with a second embodiment the control electronics is housed within a separate implantable housing which is connected via a plug connection with the implantable housing that contains the receiving coil and the rechargeable energy storage.
From commonly owned U.S. Pat. No. 6,192,272 which is hereby incorporated by reference there is known an implantable hearing system in which an electrochemical energy storage is disposed within a housing that preferably is hermetically sealed and which in turn is housed together with a control unit and a telemetry unit within an implantable housing. The energy storage can be a primary cell or a secondary cell, and in both cases can be a lithium based cell having a solid polymer electrolyte.
From commonly owned U.S. Pat. No. 6,143,440 which is hereby incorporated by reference there is known an implantable hearing system in which a rechargeable electrochemical energy storage is disposed within an hermetically tight housing. An electronic unit for monitoring the charging of the energy storage as well as a receiving coil for charging the energy storage are housed in separate housing. The hermetically tight housing of the energy storage is provided with a mechanical detector unit which is mechanically responsive to deformation due to the escaping of gas from the energy storage and which interrupts the charging process to prevent damage of the energy storage and of the housing due to impermissible operating states of the energy storage.
In commonly owned co-pending U.S. patent application Ser. No. 09/359,050 which is hereby incorporated by reference there is described an implantable hearing system, wherein a rechargeable, electrochemical energy storage which is provided with a housing is arranged within an hermetically tight housing which is equipped with a mechanical monitoring arrangement responsive to impermissible escape of gas from the energy storage and which then, if necessary, interrupts the charging process to prevent damage to the energy storage or the housing. The hermetically tight housing is arranged within a further hermetically tight housing which in accordance with a first embodiment additionally comprises an electronic unit for controlling the charging and discharging process, means for supplying a charging current and an additional electronic unit for monitoring mechanical housing monitoring arrangement. In accordance with a second embodiment these components are arranged within a separate housing, which further contains the control electronics of the hearing systems. The hermetically tight housing which contains the hermetically tight housing of the energy storage is connected to the main housing which contains the control electronics by means of a releasable, rigid mechanical connection.
From commonly owned U.S. Pat. No. 6,154,677 which is hereby incorporated by reference there is known an implantable hearing system wherein in accordance with a first embodiment a rechargeable electrochemical energy storage having a housing is arranged within an hermetically tight housing, which is provided with mechanical monitoring means responsive to impermissible escape of gas from the energy storage. In accordance with a first embodiment this hermetically tight housing of the energy storage is connected via a cable connection with an implantable main housing which contains an energy receiving coil, a corresponding electronics for control of the charging and discharging process as well as the control electronics for the hearing system. In accordance with a second embodiment the hermetically tight housing of the energy storage is housed, together with the components mentioned above, within the main housing.
From commonly owned U.S. Pat. No. 6,227,204 which is hereby incorporated by reference there is known an implantable hearing system in which the electronic unit for monitoring and controlling the charging process is designed such that the charging of the electrochemical energy storage is done dependent on the internal resistance of the energy storage, wherein during a first charging phase a constant charging current flows and during a second charging phase the charging current is adjusted such that the cell voltage that is measured during the charging process is maintained approximately at a predetermined constant value.
In commonly owned co-pending U.S. patent application Ser. No. 09/627,449 which is hereby incorporated by reference there is described an implantable hearing system with a rechargeable, electrochemical energy storage wherein the electrodes of the energy storage are arranged directly, i.e. without additional housing in an hermetically tight housing that is monitored by means of a mechanical unit responsive to impermissible gas evolution within the housing and which then mechanically interrupts the charging process. Furthermore, a temperature sensor is provided within the housing to monitor the operational state of the energy storage and, if applicable, to electronically interrupt the charging process by means of a monitoring electronics. The monitoring electronics can also be caused by the mechanical monitoring unit to interrupt the charging process. Apart form the energy storage and the temperature sensor, the monitored, hermetically tight housing of the energy storage does not contain any further components.
In commonly owned co-pending U.S. patent application Ser. No. 09/809,087 which is hereby incorporated by reference there is described a device and a process for operating a rechargeable storage for electrical energy, wherein the charging strategy of the energy storage is determined dependent on an adaptive model which takes into account data describing the state of the energy storage before start-up as well as data acquired during operation, and wherein the charging strategy can be automatically and continuously optimized using the data acquired during operation.
In commonly owned co-pending U.S. patent application Ser. No. 09/824,242 which is hereby incorporated by reference there is described an implantable energy storage arrangement for a medical implant comprising a monitoring unit that is independent of a unit for controlling the charging process and that detects the voltage of the energy storage independent of the control unit and is designed such that it assumes control over the charging path when a sensed storage voltage lies outside of a predetermined range.
In commonly owned co-pending U.S. patent application Ser. No. 09/824,212 which is hereby incorporated by reference there is described an implantable energy storage arrangement for a medical implant comprising means that is externally activatable to bypass an actuator within the charging path.
In commonly owned co-pending U.S. patent application Ser. No. 09/369,184 which is hereby incorporated by reference there is described a fully implantable hearing system for rehabilitation of a pure sensorineural hearing loss or combined conduction and inner ear hearing impairment, which system comprises at least one implantable sensor which generates an electrical audio signal, at least one signal processing and amplification unit in an audio-signal processing electronic hearing system path, at least one implantable electromechanical transducer and a unit for supplying power for the implant system, which power supply unit may comprise a secondary, rechargeable element. The hearing system is furthermore provided with an implant-side measurement unit which acquires the electrical sensor signal(s) electronically by measurement engineering and electronically conditions the signal(s). Also, a wireless telemetry unit is provided on the implant side which transfers the electronically conditioned sensor signal(s) to the outside to an external display and/or evaluation unit. In a preferred embodiment the signal processing and amplification unit, the implant-side measurement unit for generating and feeding the signals necessary for the audiometry function and the telemetry unit are housed together with the power supply unit in a hermetically tight and biocompatible implant housing to form an electronic module.
When the electrochemical secondary cell(s) is/are arranged within a separate hermetically gas tight protective housing that prevents the escape of substances from the cell which might be toxic to the electronics of the implant system and/or of gases which might damage the electronics and/or might lead to an impermissible pressure rise within the implant housing, and/or if a detector is provided that is in mechanical connection with the protective housing of the cell and which interrupts further supply of energy during the charging process and/or also interrupts the discharging process in cases of an impermissible or unwanted operational state, such additional protective measures cause additional costs, are troublesome in particular from a constructional point of view and increase the space requirements of an active implant. The latter can be of particular disadvantage when the implant is to be applied to a body region in which, by nature, there is only very little space available. This applies in particular to the implants for rehabilitation of a hearing disorder which were described in detail above, wherein in most cases the electronic module is positioned in the region of the mastoid on the scull cap, in which case the requirement is of particular concern that the size of the implant should be as small as possible. Especially in such a case the protective measures mentioned above are of particular disadvantage because often space in the direction of the height of the implant is required.
The primary object of the present invention is to devise an implantable medical device that is constructed as simple as possible but yet provides for sufficient operational safety with respect to the energy storage.
In accordance with the invention this object is achieved in that in an implantable medical device comprising an hermetically sealed housing which houses an electronic unit and an electrochemical energy storage for supplying electrical current to the medical device, the energy storage is disposed directly within the hermetically sealed housing and does not have a separate housing. The solution in accordance with the invention is advantageous in that due to the energy storage being arranged directly within the hermetically sealed housing and not having a separate housing, the construction is made more simple and therefore the production of the implantable medical device is facilitated.
In preferred embodiments of the invention the energy storage is a lithium based battery with solid electrolyte system, which battery is monitored with respect to its operational state by the electronic unit to prevent damage of the electronic unit. This is of particular importance when the energy storage is a rechargeable battery. Preferably the electronic unit further serves to control the medical device.
These and further objects, features and advantages of the present invention will become apparent from the following description when taken in connection with the accompanying drawings which, for purposes of illustration only, show several embodiments in accordance with the present invention.